Download Alkaline and Related Rocks: A Glossary of Names

Alkaline and Related Rocks: A Glossary of Names
This glossary is only a rough guide to the bewildering nomenclature of alkaline and related rocks.
“Subtleties”, like the chemistry of a specific mineral, are very important for finding the right name for
your rock. The list presented here is by no means exhaustive and includes only the most frequently
used terms. Please refer to Le Maitre (2002) for the IUGS-endorsed rock-classification guidelines
and further details.
Agpaite
(agpaitic
foid syenite)
Any peralkaline feldspathoid syenite containing Na and/or K titano-,
zircono- or niobosilicates (such as lorenzenite, eudialyte, lamprophyllite,
murmanite, wadeite, lovozerite, etc.). The enrichment of agpaitic rocks in
“incompatible” elements may also be reflected in the composition of their
major constituents (e.g., high Zr content of aegirine, etc.). For Appat,
Ilímaussaq complex, South Greenland.
Alkali basalt
A collective term for extrusive mafic rocks containing modal or normative
feldspathoids (usually nepheline). Olivine and Ti-rich augite are the dominant
ferromagnesian silicates in these rocks. For enrichment of these rocks in
alkalis relative to subalkali basalts; the etymology of the term “basalt” is
uncertain.
Basanite
A collective term for extrusive mafic rocks containing essential modal or
normative feldspathoids (usually nepheline) and olivine. Etymology uncertain.
Carbonatite
Igneous rock containing >50% modal carbonate (usually calcite,
dolomite or ankerite) and various ferromagnesian silicate minerals
(olivine, monticellite, clinopyroxenes, calcic amphiboles or biotite).
Characteristic accessory constituents (gaining locally the status of rockforming minerals) are magnetite, fluorapatite, pyrochlore, ilmenite,
perovskite, titanite and rare-earth (fluoro)carbonates. Carbonatites are
further classified on the basis of their texture and mineralogy or majorelement chemical composition (e.g., alvikite, calcite carbonatite,
natrocarbonatite, etc.). For the predominance of carbonates in the
mineral mode.
Essexite
Nepheline monzogabbro or monzodiorite consisting of augite, intermediate
plagioclase and calcic amphibole (typically kaersutite) with lesser amounts of
alkali feldspar, nepheline and olivine. For Essex Co., Massachusetts, USA.
Fergusite
A variety of foidolite containing essential clinopyroxene and 30-70% modal
leucite (typically replaced by a mixture of nepheline, alkali feldspar, kalsilite
and analcime). For Fergus Co., central Montana, USA.
Feldspathoid
(foid) syenite
A collective name for phaneritic rocks containing 10-60% of nepheline,
sodalite, or any other feldspathoid mineral among their light-colored
silicate constituents. Foid syenites are further classified on the basis of
their mineralogy, bulk-rock chemistry and texture (e.g., sodalite syenite,
peralkaline agpaitic nepheline syenite, lujavrite, etc.). For the presence
of essential feldspathoids in their modal composition and affinity to
syenite, i.e. an alkali-feldspar rock from Syene (Aswân, southern Egypt).
Foidolite
A collective name for phaneritic rocks containing > 60% of nepheline,
leucite, or any other feldspathoid mineral among their light-colored
silicate constituents. Foidolites are further classified on the basis of their
mineralogy (e.g., nephelinolite, urtite, italite, etc.). For the
predominance of feldspathoid (foid) minerals over feldspars and λίθος =
stone (Ancient Greek).
Foskorite
See Phoscorite.
Foyaite
Massive or trachytoidal hypersolvus nepheline syenite (commonly
peralkaline). For Mt. Foia, Monchique, western Algarve, Portugal.
Ijolite
A variety of foidolite containing essential clinopyroxene (diopside,
aegirine-augite or aegirine) and 30-70% modal nepheline; apatite,
Ca-Fe-Ti garnets, biotite, titanite, magnetite and perovskite are common
minor constituents. For R. Iijoki, northern Finland.
Italite
A variety of foidolite in which leucite is the predominant feldspathoid
mineral and ferromagnesian silicates comprise 30 modal % or less of the rock.
For Italy.
Kakortokite
Cumulate-textured peralkaline nepheline syenite typically showing alkalifeldspar-, arfvedsonite- and eudialyte-rich layers. For Quaqortoq,
Ilímaussaq complex, South Greenland.
Kamafugite
A collective name for extrusive potassic ultramafic rocks (2.0-8.5 wt.% K2O, 818 wt.% MgO, 33-44 wt.% SiO2) commonly containing modal or normative
kalsilite. All members of the clan contain either clinopyroxene or olivine as their
dominant mafic constituents, and, in addition to kalsilite or leucite, may also
contain melilite. These rocks are further categorized on the basis of their
mineralogy (e.g., mafurite = olivine-clinopyroxene foidite with kalsilite as the
principal feldspathoid mineral; ugandite = clinopyroxene-olivine leucitite). For
katungite, mafurite and ugandite, the three earliest-recognized members of the
clan from different localities in Uganda.
Kimberliite
Potassic ultramafic rock with a high content of volatiles (especially CO2)
containing xenolithic material from the mantle and crust, as well as minerals
liberated from these xenoliths (i.e. xenocrysts, including diamond) and those
precipitated from the parental kimberlitic magma and its derivative fluids at
different stages in the evolution history of the host rock. The latter category
includes some of the macrocrysts, as well as (micro)phenocrysts, groundmass
constituents and late-stage minerals developed at the expense of primary
magmatic phases. Kimberlites commonly show an inequigranular texture
arising from the presence of xenoliths and macrocrysts (> 0.5 mm), although
aphyric aphanitic kimberlites also occur. The macrocryst suite typically
includes olivine, pyroxenes, phlogopite, ilmenite and pyrope. The matrix of
hypabyssal kimberlites typically comprises crystals of olivine, monticellite,
phlogopite, perovskite, spinel-group minerals (ranging in composition from Mgrich chromite to Mg-rich ulvöspinel to Fe-rich spinel to Ti-rich magnetite) and
apatite immersed in a carbonate-serpentine mesostasis. For Kimberley,
Northern Cape, South Africa.
Lamproite
Peralkaline ultrapotassic rocks with a wide range of SiO2 (typically 34-58
wt.%, but up to 68 wt.% in some varieties) and MgO values (typically, 527 wt.%), characterized by the presence of certain K-rich minerals (e.g.,
Ti-rich and Al-poor phlogopite, Fe-rich leucite, priderite) and absence of
certain other minerals incompatible with the ultrapotassic nature of
lamprotic magmas (e.g., liquidus plagioclase, nepheline, melilite and
calcic garnets). Lamproites are further classified on the basis of their
mineralogy and textural characteristics (e.g., glassy olivine-lamproitic
tuff, diopside-leucite-phlogopite lamproite, etc.). For λαµπρός = bright
(Ancient Greek).
Lamprophyre
Porphyritic meso- to melanocratic rocks forming shallow intrusions
(rarely extrusive units) and containing phenocrysts of biotite, amphibole,
clinopyroxene or olivine set in a matrix consisting of potassium feldspar,
plagioclase, foids, calcite, Fe-Ti oxides and various ferromagnesian
silicates. Lamprophyres are further classified on the basis of their
mineralogy (e.g., monchiquite, camptonite, etc.). For λαµπρός = bright
(Ancient Greek) and in allusion to their biotite-/amphibole-phyric nature.
Leucite
phonolite
See Phonolite.
Leucitite
A collective name for extrusive rocks containing essential modal or normative
Leucite; if other feldspathoid minerals (e.g., nepheline) are present, leucite
has to predominate. Leucitites can be further classified on the basis of their
mineralogy (e.g., ugandite = melanocratic clinopyroxene-olivine leucitite). For
the presence of essential leucite in their composition.
Lujavrite
Meso- to melanocratic trachytoidal peralkaline nepheline syenite
(commonly agpaitic). For Lujavr Urt (Lovozero Mts.), Kola P-la,
northwestern Russia.
Melilitite
A collective name for extrusive and shallow intrusive rocks containing >
10% modal melilite, devoid of kalsilite and, if other feldspathoid minerals
are present, F < melilite. Extrusive rocks of indeterminate modal
composition, but containing > 10% normative larnite (Ca2SiO4) are
classified as melilitite, potassic melilitite or olivine melilitite depending on
their Na/K ratio and proportion of olivine in their composition. For the
presence of essential melilite in their composition.
Melilitolite
A collective name for plutonic rocks containing > 10% modal melilite
and, if feldspathoid minerals are present, F < melilite. Melilitolites
commonly contain olivine, clinopyroxene, perovskite, nepheline, or
haüyne, and can thus be further classified based on the relative
proportion of these minerals (e.g., kugdite, okaite, etc.). For the
presence of essential melilite in their modal composition and λίθος =
stone (Ancient Greek).
Melteigite
A variety of foidolite containing essential clinopyroxene (diopside,
aegirine-augite or aegirine) and 10-30% modal nepheline; apatite,
Ca-Fe-Ti garnets, biotite, titanite, magnetite and perovskite are common
minor constituents. For Melteig Farm, Fen carbonatite complex, Telemark,
southern Norway.
Miaskite
Leucocratic hypersolvus foid (monzo)syenite containing calcic
albite, perthite, and nepheline ± cancrinite-group minerals as the
principal foid minerals. Biotite is the major mafic mineral, while ilmenite,
zircon and pyrochlore are characteristic accessory constituents (cf.
Agpaite). For Miass, South Urals, Russia.
Missourite
A variety of foidolite containing essential clinopyroxene and 10-30% modal
leucite; olivine is also commonly present. For R. Missouri, Montana, USA.
Naujaite
Agpaitic (nepheline-)sodalite syenite with a poikilitic texture comprising crystals
of feldspathoid minerals enclosed in alkali feldspar and ferromagnesian
silicates. For Naajakasik (formerly Naujakasik), Ilímaussaq complex, South
Greenland.
Nephelinite
A collective name for extrusive rocks containing essential modal or
normative nepheline and little or no feldspar. If other feldspathoid
minerals (e.g., leucite or analcime) are present, nepheline has to
predominate. Phenocrysts of clinopyroxene (augite, diopside and
aegirine-augite), titanite and Ca-Fe-Ti garnets, and groundmass aegirine
are common. For the presence of essential nepheline in their
composition.
Orangeite
(Group-II
kimberlite;
micaceous
Peralkaline ultrapotassic volatile-rich rocks superficially similar to kimberlites,
but distinct from the latter in lacking monticellite, Mg-rich ulvöspinel and
kinoshitalite, and containing abundant phlogopite (as macrocrysts, microphenocrysts and groundmass grains) and clinopyroxene microphenocrysts
kimberlite)
(commonly, diopside mantled by Ti-rich aegirine-augite). Sr-, Zr- and rareearth-bearing minerals (perovskite, apatite, Ca-Fe-Ti garnets, etc.) are
characteristic accessory constituents in the groundmass. For the Orange Free
State (now Free State), central South Africa.
Phonolite
An extrusive analogue of feldspathoid syenite; if the dominant
feldspathoid is other than nepheline, a mineral modifier must be added
to the root name (e.g., leucite phonolite). Apparently, for the high-pitch sound it
makes when struck with a hammer: ϕωνή = voice and λίθος = stone (Ancient
Greek).
Phonolitic
foidite
A collective name for extrusive rocks containing essential modal
feldspathoids and subordinate amounts of feldspar (typically, as a
groundmass phase). Phenocrysts of clinopyroxene (augite, diopside and
aegirine-augite) and titanite are common. Depending on their
predominant feldspathoid minerals, these rocks can be further classified
as phonolitic nephelinite, phonolitic leucitite, etc. For their modal
composition, “intermediate” between foidites and phonolites.
Phoscorite
Plutonic rock containing essential magnetite, apatite and either forsterite
or phlogopite; some researchers extend this term to incorporate rocks
with essential diopside. Phoscorites are almost invariably found in
association with carbonatites, and commonly contain minor amounts of
calcite and accessory Ti, Nb and Zr oxides (baddeleyite, pyrochlore,
zirconolite, etc.). For the Phosphor Development Corporation of South
Africa.
Pulaskite
Nepheline-bearing alkali feldspar syenite. For Pulaski Co., central
Arkansas, USA.
Shonkinite
A melanocratic variety of feldspathoid syenite containing a large
proportion (> 60% modal) of mafic silicates (typically, augite, biotite and
olivine) and < 10% modal feldspar. For Shonkin, the Native-American
name for the Highwood Mountains, Chouteau Co., central Montana, USA.
Silicocarbonatite
A variety of carbonatite which contains > 20 wt.% SiO2 in its bulkrock chemical composition. In addition to carbonates,
silicocarbonatites contain significant amounts of ferromagnesian
silicates (forsterite, diopside, aegirine-augite, phlogopite, or calcic
amphiboles). For the chemical composition and affinity to
carbonatites.
Sodalitolite
See Tawite.
Tawite
A variety of foidolite in which sodalite is the predominant feldspathoid
mineral. For R. Tavajok, Lovozero Mts., Kola P-la, northwestern Russia.
Teschenite
(teschinite)
Analcime gabbro; typically comprises calcic plagioclase, augite, olivine and
analcime. For Cieszyn and Český Těšín (Teschen in German) at the border
between Poland and Czech Republic.
Theralite
Nepheline gabbro; typically comprises calcic plagioclase, augite, nepheline
and variable amounts of olivine. Etymology uncertain; allegedly, for the relative
rarity of this rock type (from the Ancient Greek for “to pursue”).
Urtite
A variety of foidolite containing > 70% modal nepheline; clinopyroxene,
apatite, titanite, magnetite and perovskite are commonly present in
subordinate amounts. For Lujavr Urt, (Lovozero Mts.), Kola P-la,
northwestern Russia.